The present invention relates to an electromagnetically actuated spring clutch having an integrated sensor activated control circuit for selectively engaging and disengaging the clutch.
Electromagnetically actuated spring clutches are useful components in machines such as photocopiers, etc. for causing precise angular and linear movements of various moving parts in machines. For example spring clutches might be used for positive positioning of parts, two speed transmissions, reversing applications, paper registrations, paper feeding and cam positioning.
There are several different embodiments of spring clutches. In one embodiment the clutch is normally engaged. For example in U.S. Pat. No. 3,926,286, to disengage the clutch, the spring is released from its initial driving contact with the input hub by means of an exterior floating sleeve which contacts the free end of the spring. Stopping rotation of the sleeve expands or unwraps the spring so that torque is no longer transmitted to the output hub whereby the clutch is no longer engaged.
In yet another embodiment of a spring clutch, the clutch is normally disengaged. For example in U.S. Pat. No. 3,185,276, the action of a sleeve is employed to initiate wrap down of the spring rather than release of the spring. Wrap down of the spring causes the clutch to become engaged. These are but a few of the many examples of spring clutches.
Electromagnetically actuated spring clutches employ an electromagnetic coil to control the release and/or wrap down of the spring. One such normally disengaged electromagnetically actuated wrap spring clutch is shown in U.S. Pat. No. 4,263,995, where a wrap spring is caused to wrap down onto input and output hubs by a magnetic field acting between a control ring and an adjacent shoulder ring affixed to the output hub and forming a section of the flux path. The remaining sections defining the magnetic flux path and enclosing the electromagnetic coil are fixed in position, only the two ring.sub.s being rotatable. The magnetic field is caused by energization of the electromagnetic coil. U.S. Pat. No. 5,133,437 shows a similar electromagnetically actuated spring clutch which includes a brake.
Oftentimes it is necessary to effect indexing of the spring clutch output member to a plurality of angularly spaced positions and/or revolutions of the clutch. U.S. Pat. No. 4,191,283 is an example of a normally engaged mechanically indexed spring clutch. In this patent, a solenoid actuated interposer mechanically engages a rotatable member of the spring clutch to stop the rotatable member in a plurality of positions, thereby disengaging the clutch.
Existing methods of indexing spring clutches often have many drawbacks and undesirable features. For example, currently available indexing spring clutches typically are rather bulky and take up precious space. Moreover, they have many additional working parts which adds to their expense of manufacture, assembly and installation. Many designs do not readily provide for returning to a home position. In slow input speed and/or high friction load applications, the normally engaged, mechanically indexed spring clutches often exhibit wear due to insufficient over run which results in the spring being only partially disengaged, thereby causing premature failure.
These are but some of the problems associated with existing indexing clutches.